Piston



Patentedl Oct. 14, 1930 -UNITED STATES PATENT OFFICE WILLIAM G. CALKINS, 0F DETROIT, MICHIGAN, ASSIGNGR TO CHRYSLER CORPORA- TION, 0F DETROIT, MICHIGAN, A CORPORATION 0F DELAWARE PISTON Application led April 20,

This invention relates to pistons and more particularly to a composite piston having a head section of a metal of a given coeiiicient of expansion and a skirt section of a metal/of a different coeiicient of expansion.

In the manufacture of pistons it is desirable to reduce the weight to a minimum thereby minimizing bearing pressures and reducing vibration. An aluminum alloy piston is light in weight but due ,to the high coeiicient o expansion of the aluminum considerable diicult .has been experienced with the skirt section ecause of its expansion at high temperatures. It is desirable therefore to make the skirt section of a' metal, such as cast iron, havin a less coeiicient of expansion than the a uzminum alloy. A composite piston having an aluminum alloy head section and a cast iron skirt section is suiiciently light in weight and maintains the advantages of the full cast iron piston.

I-Ieretofore, the connection between the head section and the skirt section of a composite piston has presented several problems; the conduction of heat from the head section to the skirt, mechanical distortion of the skirt section due to the thermal expansion of the head section, and the thermal expansion of the connecting means where such is used.

It is an object of this invention to provide a Piston head section havin a high coefficient o expansion and securing t ereto a full skirt section having a lower coeiioient of expansion; the head section also having a high rate of heat conductivity in order to maintain low head temperatures permitting the use of high compression ratios and high speeds. v

Another object of the invention is to unite the head section with the skirt section in such a manner that the head section is mechanically free from the skirt section at the outer periphery so that thermal expansion of thel head section does not cause mechanical distortion of the skirt section. Thek head section is thermally insulated from the skirt section in so far as practical.

A further object of the invention is to form the piston pin bosses integral with a full cast iron skirt so that the thermal heat conduction and thermal expansion of the 1928. Serial No. 271,617.

head section does not effect the bearin conditions with reference 4to clearance an distortion.

Another object of the invention is to fasten a head section having a high coefficient of expansion to a skirt section having a lower coefficient of expansion by a means provided to compensate for the differential expansion rate of the two members.

Other objects and advantages will more fully appear from the following description taken in connection with the accompanying drawings in which: v

Fig. 1 is a vertical sectional view of my improved piston.

Fig. 2 is a view corresponding to Fig. 1 showing a modification of my invention.

Fig. 3 is a perspective view of a compensating member utilized in my invention.

Referring to the drawings, I have shown a piston having a head sect-ion 10 made of a metal having a high coeicient of expansion and a high rate of heat conductivity, preferably cast from an aluminum alloy. The central portion of the head section 10 is provided with a boss 12 having an opening 14 to receive a securing means such as a bolt 16. A counterbore 18 is provided to receive the head 20 of the bolt 16. The outer periphery of the head section is provided with an annlar flange 22 which receives piston rings 2 y Improved results have been found by the particular combination and arrangement of rings shown in the drawings. The upper ring comprises a two part ring 24, each part having adjacent flanges 26 overlapping a tongue 28 in the rin roove 30. T e central ring 32 is provi e with a groove 34 at its lower outer corner. The lower ring 36 is providedwith radial openings 38 through which lubricant may pass from the cylinder wall to an opening 40 in the flange 22 where it may drain back into the crank case. The upper ring 24 is ideal for a compression ring as the compression forces find their way into the ring groove 30 and force the rings outwardly against the cylinder wall.

The central ring 32 scrapes the lubricant from the cylinder wall and the lower ring drain away from The skirty section preferably made :from

a nickel-chrome alloy cast iron or a high tensile pearlitic iron. This metal has a'low coeliicient of expansion as compared with the aluminum alloy head and the pistonr skirts may be made with sli ht clearances.

A full cylindrical skirt provi guide in all directions and is caring characteristics.

Wrist pin' bosses 50 are formed .integral with the skirt section 44 and are independent of the head section so that the thermal expansion'of the head section does` not mechanically distort the bosses 50. The head section is'fastened to the skirt section by a means whichl compensates for the differential expansion rates of the two metals. In the form shown in Fig. 1 a steel bolt 16 is used, extending through the aligned openings 14 and 48. A concave washer 52, preferably made of spring steel, is placed over the threaded end of the bolt 16 with its outer periphery in engagement with the under surface of the head portion 42 and a nut v54 screwthreaded on the bolt 16 engages the central portion of the con-- cave member 52. 'A Cotter key 56 prevents turning the nut 54. The form shown, however, is preferable as it does not unbalance the piston.

As the head section expands, the bolt 16 is carried with the upper outersurface ofthe es a cros's head uniform 1n its head section and slides through the opening 48 inl the'head portion 42 of the skirt section compressing the resilient member 52. If the parts, were rigidly secured at this point, the would cause'the bolt or the head portion to break vor distorta f The outer surface of the boss 12 may extend slightly beyond the outer surface of the flange b 22 so that the point of contact between the lhead section andthe skirt section is at the center. The important thing is lthat the head is mechanically free from the skirt section at the outer periphery so that the head s ectliont expands radially independent of the S 1I The head section is practically thermally insulated from-the skirt so that there is butslight thermal expansion of the skirt and no mechanical distortion of the skirt due to theI thermal expansion of the head section.

expansion of the head section If desired the head section may be forged from ahigh Astrength aluminum alloy and al threaded projection formed on the. end of the boss12, as shown in Fig.'2. In this form the differential expansion between the two lmetals is less and there is less movement of the resilient member 52. A shoulder 62 is provided on the projection 60 to form a stop for the central portion of the resilient membei 52 or the nut 54 so that the parts may'not be drawn together to prevent the movement ofthe projection 60 in the opening 48. This ysame plan may be followed on the construction shown in Fig. 1. On the other hand, if desired, the stop may be omitted, the 'nut screwed in until the center of the washer bottoms on the head 42 and then the nut may be backed ofi" a pre-determined amount so as to leave a certain tension on the'spring washer anda certain clearance between the center of y the washer andthe bottom of the head 42.

It will be obvious that various changes may be made in the arrangement, combination and construction of the various parts of my improved device` Without departing from the spiiit of my invention and it is my intention to cover by my claims such changes as may reasonably be included within the scopethereof.

What I claim, is:

1. A piston of the class described comprising, a head section having a given coefi'icient of expansion, an annular flange at the outer periphery of said head section, a boss on the axial line through said head section, said boss having its outer surface extending slightly beyond the outer surface of said flange, a skirt section having a lower coefficient of expansion than said head section, wrist pin bearings and a flat head portion integral with said skirt section, and means carried by said boss4 including an expansible connecting member .for vieldably securing said head section and said skirt section together.

2. A piston ofthe class described comprising, an aluminum alloy head section, an iron alloy skirt section having a fiat head -portion provided with a plurality of openings one of which is on the axial line through said piston, a central engaging portion on said head section adapted for engagement with the upper surface of the skirt head portion, a memer having a diameter less than the diameter of the central engaging portion projecting from said engaging portion to be received in the axial` opening in the head portion, a screwthreaded member on the outer end of said projection, and a spring steel member between said screwthreaded member and the lower surface of the head portion of said skirt section.

3. A piston of the class described comprising, a head section havin a given coecient coeiiicient of expansion, an end wall on said its ias

lmi

skirt section having a central opening therein, an annular flange' at lthe cuter periphery of said head section free for `radial expansion .with respect to the `outer periphery of said skirt-section, a 'central portion on said head section extending beyond the outer extremity of said flange adapted for engagement with the upper surface of the endvwall of said skirt section, a member projecting from said engaging portion Vto be received in the central opening in said end Wall, a screwthreaded member on the outer end of said projection, and a spring steel member between said screwthreaded member and the lower surface ofthe end wall of said skirt portion.

4. A piston including a head part having a peri heral flange and a central boss vextending slightly beyond the outer extremity of sald flange, a skirt part having an end Wall bearing against the end of said boss, the extremity of said flange being held against contact with said end wall during thermal expansion ofsaid flange by the corresponding expansion of said boss', and meansv on said boss coacting with said end wall for securing said skirt and head parts together.

5. A piston includlng a head part having a peripheral flange and a central boss extending slightly beyond the outer extremity of said flange', a skirt part having an end wall bearing against the end of said boss, the extremity of said flange being held a ainst contact with said end wall Vduring t ermal expansion 'of said flange by the corresponding expansion of said boss, a stem on saidboss extending through an aperture in said end wall, and a yieldable member on said stem engaging the inner'side of said end Wall and yieldably securing said head and skirt parts together.

WILLIAM G. CALKINS. 

